In general, heat radiating components for dissipating heat which is generated by a semiconductor element such as a semiconductor laser element or an LSI chip, are well known. For example, the range of application of a semiconductor laser is rapidly widening in the field of optical communication, optical memories and the like. As a result, efforts have been made to increase the output or reduce the wavelength of such a semiconductor laser. Under such circumstances, the heat generating value of a semiconductor laser element is apt to be increased, whereby the reliability of the semiconductor laser element is disadvantageously deteriorated and its life is reduced. To avoid these problems, there has been developed a semiconductor laser which is provided with a heat radiating component of a heat conductive material, in order to dissipate heat generated by the semiconductor laser element.
FIG. 1 is a block diagram showing a conventional semiconductor laser which is provided with a heat radiating component. Referring to FIG. 1, the conventional semiconductor laser comprises a stem 4, a submount 5 which is mounted on a prescribed upper surface region of the stem 4 through a brazing filler metal 6, and a semiconductor laser element 1 which is mounted on a prescribed upper surface region of the submount 5 through another brazing filler metal 2. The brazing filler metal 6 is adapted to bond the submount 5 to the stem 4, while the other brazing filler metal 2 is adapted to bond the semiconductor laser element 1 to submount 5. Table 1 shows materials and shapes of the semiconductor laser element 1, the submount 5, the brazing filler metals 2 and 6, and the stem 4 respectively.
TABLE 1 ______________________________________ Element 1 Material: Compound Semiconductor Composed of Ga, As, In, P, Al or the like Shape: up to 0.5 mm square Submount 5 Material: Si, AlN, BeO, Cu--W Alloy, Cu--Mo Alloy, SiC, cBN polycrystalline Substance or Single-Crystalline Diamond Shape: up to 1 mm square, 0.2 to 0.5 mm thick Brazing Element Side Au--Sn Alloy, Pb--Sn Filler (2): Alloy or In Metals 2 & 6 Stem Side (6): Au--Si Alloy or Pb--Sn Alloy Stem 4 Material: Cu, Cu--W Alloy, Cu--Mo Alloy or Cu--W--Mo Alloy Shape: 5 to 15 mm square ______________________________________
In operation, heat which is generated by the semiconductor laser element 1 is transmitted to the stem 4 through the submount 5 for dissipation. The submount 5 is adapted to efficiently transmit the heat generated from the semiconductor laser element 1 to the stem 4. Therefore, the submount 5 is made of a material having a high thermal conductivity, such as a Cu-W alloy, a polycrystalline substance of cBN (cubic boron nitride) or single-crystalline diamond shown in Table 1, for example.
In the conventional semiconductor laser, however, the brazing filler metal 6 is interposed between the submount 5 and the stem 4, to inevitably resist against the thermal conduction from the submount 5 to the stem 4. In the conventional semiconductor laser, therefore, it has been difficult to attain an efficient heat radiation or dissipation due to such interposition of the brazing filler metal 6.
When the submount 5 is made of high-priced single-crystalline diamond or the like, its size is considerably reduced as compared with the upper surface of the stem 4. Consequently, the thermal conduction surfaces of the submount 5 and the stem 4 are so reduced that thermal diffusion mainly progresses vertically along the direction of depth of the stem 4 and no sufficient thermal diffusion is attained in the transverse direction. Also when the submount 5 is made of single-crystalline diamond, it is difficult to attain a sufficient heat radiation efficiency.
On the other hand, the brazing filler metal 2 which is interposed between the submount 5 and the semiconductor laser element 1 is made of an Au-Sn alloy, a Pb-Sn alloy or the like. However, such a material has a high thermal expansion coefficient. When the temperature of the semiconductor laser element 1 is increased during operation, the semiconductor laser element 1 is extremely distorted by heat. Such heat distortion leads to an abnormal operation of the semiconductor laser element 1 or to a reduction of its operational life.
In general, therefore, it has been difficult to provide a heat radiating component which has an excellent radiation effect and a semiconductor laser which has excellent operation characteristics. Further, it has been difficult to effectively prevent the heat distortion of a semiconductor element such as a semiconductor laser element or an LSI chip, which is bonded by a brazing filler metal having a high thermal expansion coefficient.